1. Field of the Invention
The present invention relates generally to architectures for optical signals, and more particularly to time compensation architectures for controlling timing of optical and optoelectronic signals.
2. Description of the Art
The telecommunications industry is rapidly switching from electronic systems to hybrid platforms which utilize both electronics and photonics to increase the operational bandwidth. Today""s electronic communication systems consist of electrical networks, microwave amplifiers, microwave transmitters, and high speed semiconductor receivers. There are numerous electrical devices available so this architecture works well in the confines of electronics. In these electronic systems a passive technique to control timing (e.g., phasing) of signals currently utilizes an electronic stripline with an impedance load. This technique is limited because the intrinsic dispersion associated with the stripline broadens short electrical pulses that are less than 10 ps in duration. This broadening will ultimately limit the speed of the host system. Eventually as optical systems come into use, purely optical signal processing devices will be required.
What is needed, therefore, is a time compensation architecture employing optical devices as a controllable delay.
The present invention involves a time compensation architecture employing an optical device as a controllable delay.
The optical time compensation architecture utilizes the material index of refraction, n, and material lengths to control the relative timing of optical signals. The optical delay through the media can be described by
t=n*l/c
where t is the time delay, n is the index of refraction, l is the material length, and c is the speed of light. The relative timing (xcex94t12) of two signals can be controlled by either changing the indices of refraction (n1, n2), or the material lengths (l1, l2), or both. It follows that
xcex94t12=(n1*l1xe2x88x92n2*l2)/c.
Of course this technique is extendable to a plurality of delays where the index of refraction and/or the material length is controllable for each individual signal.
While passive compensation techniques have a large number of applications, active control of relative signal timing may be necessary for real time signal processing. Active techniques to control the time or phase delay of an optical beam in fiber optical systems currently include piezo-electric fiber stretching, electro-optic phase modulators, and current injection in semiconductor waveguides. These techniques suffer from slow time response (typically 10 KHz), inability to produce large temporal delays (typically 20 femtoseconds), and the inability to produce precise controllable delays, respectively.
These deficiencies can be overcome by using optically pumped photoactive systems such as doped fibers, and semiconductor or polymer waveguides where the amplitude of the pump laser alters the index of refraction of the material at the signal wavelength. In this case the dynamic timing change (xcex4T) is given by
xcex4T=xcex4n*l/c
where xcex4n is the pump induced index change.
Index of refraction changes producing hundreds of picosecond delays with sub femtosecond resolution are realizable in such optically pumped systems. In addition, index of refraction changes based on ground and/or excited state absorption processes or nonlinear optical interactions can ultimately produce control frequencies in excess of 1 THz.
Briefly, the present invention comprises time compensation architecture for use with a plurality of optical signals. It comprises means for receiving the plurality of optical signals, optical means for selectively delaying the propagation of each of the plurality of optical signals, and means for outputting the time delayed optical signals. The delay may be achieved by changing the indices of refraction or the material lengths of the elements and can either be an active or a passive compensation technique.
The foregoing and additional features and advantages of this invention will become apparent from the detailed description and accompanying drawing figures below. In the figures and the written description, numerals indicate the various elements of the invention, like numerals referring to like elements throughout both the drawing figures and the written description.